This invention relates to a field emission cold cathode for use as in a flat panel display and a method for the production thereof.
In the field of vacuum microelectronics, the development of field emission cold cathodes discharging electrons through minute emitters of a projecting structure is being promoted positively by the utilization of the technology on the fabrication of semiconductors which has been advancing rapidly in recent years.
As a typical example of the outcome of the development, the technique disclosed by C. A. Spint et al. in "Journal of Applied Physics," Vol. 47, 5248 (1976) has been found as widespread recognition.
The method for producing a field emission cold cathode by this technique is illustrated in FIG. 9. This method produces the field emission cold cathode as follows.
First, a SiO.sub.2 layer 203 is formed on a Si single crystal substrate 201 by the technique of depositing such as CVD. A Mo layer 205 destined to serve as a gate electrode and an Al layer 207 destined to serve as a sacrifice layer are formed thereon as by the technique of spattering and the technique of oblique vacuum deposition, and then an opening 211 approximately 1.5 .mu.m in diameter is incised in the superposed layers as by the technique of etching as illustrated in FIG. 9A.
Then, a metal such as, for example, Mo which is destined to serve as the material for an emitter 213 is vacuum deposited on the Si single crystal substrate 201 in a direction perpendicular to the Si single crystal substrate 201 while keeping the whole of the Si single crystal substrate 201 in rotation, with the result that the metal (Mo) is deposited in a conical shape in the opening 211 and allowed eventually to form the emitter 213 as illustrated in FIG. 9B. Since the metal (Mo) is gradually deposited meanwhile on the sacrifice layer 207, the opening 211 is occluded with the growth of the emitter 213. The formation of the emitter 213 is terminated when the opening 211 is wholly occluded.
Thereafter, the metal (Mo) layer, the sacrifice layer 207, etc. which have been deposited are removed to expose the gate electrode layer 205 as illustrated in FIG. 9C. Thus, a field emission cold cathode possessed of the conical shape emitter 213 is formed.
Then, the principal part of a device is formed by having an anode (omitted from illustration) opposed across a desired interval to the emitter 213.
The structure of the conventional field emission cold cathode and the method employed for the production thereof, however, mainly entail the following problems.
In the conventional method, the deposition of a metal for the conical shape emitters in the opening 211 is effected while keeping the whole of the Si single crystal substrate 201 in rotation. Since the formation of the emitter 213 is controlled by utilizing the gradual occlusion of the opening 211, it is extremely difficult to attain accurate control of the shape of the tip of the emitter 213, the height of the emitter 213, etc. The emitters 213 in each of the field emission cold cathodes thus produced, betray bad uniformity in the shape and the height and, consequently, the production of field emission cold cathodes suffers from a poor yield because of inferior reproducibility of the shape of the emitters. Particularly, when a multiplicity of field emission cold cathodes of one identical shape are to be arrayed on one and the same substrate, therefore, the cost of production is conspicuously high.
Further, owing to the bad uniformity in the shape and the size of the emitters 213, the uniformity of field emission is low. Moreover, since the emitters 213 are deficient in the sharpness of tip which is necessary for field emission, the field emission cold cathodes suffer from unduly low field emission efficiency and unduly large electric power consumption.
The conventional technique forms the SiO.sub.2 layer 203 in a large thickness as by the CVD, superposes the gate electrode layer 205 thereon, and, in the subsequent formation of the emitter 213 thereon, deposits the metal as the material for the emitter 213 once and removes the deposited metal afterward. Thus, the distances between the gates and the emitters which constitute one main factor for deciding the field emission efficiency cannot be easily controlled accurately. In the field emission cold cathodes to be produced by the conventional method, therefore, the field emission efficiency and the operating characteristics are both dispersed widely.